RU2136112C1 - Method for packet exchange in lan - Google Patents

Abstract

FIELD: information exchange in local-area networks. SUBSTANCE: method involves relative synchronization of workstations, splitting real time into segments of equal duration each of which is equal to T_s>= 2t_sp+t_rg, where t_sp is signal spreading period between two most remote workstations in LAN, t_rg is period for recognition of carrier from other stations in shared channel, detection of business of shared channel at each station using analysis of carrier. In case if shared channel is busy, method involves analysis of carrier and shifting start of "own" segment, when shared channel is released. This involves shifting the time scale for period of channel busy condition, in case of recognition at station for its interval T_s of information transmission from other stations in network and presence of information for its synchronous transmission using arbitrary length packets so that beginning of each packet is equal to beginning of packet which is following after "own" segment. Transmission of packet is finished during interval which is equal to T_p. EFFECT: increased throughput of shared channel for low traffic and unlimited information amount to be transmitted in packet. 3 dwg

Description

 The invention relates to the transmission of information between logical entities, for example, in local networks, in particular, to methods of packet exchange in shared channels.

 In local networks, a significant number of subscriber stations can be connected to a shared channel. A prerequisite for the effective use of the bandwidth of the collective channel in the interests of all subscribers of the network is to ensure the alternate transmission of information from those subscriber stations that have information for transmission. It must be borne in mind that if for the transmission of packets some order is needed for the subscriber stations to enter the collective channel for transmitting packets, then all stations constantly receive information in the network.

 The method of packet exchange determines the functioning of subscriber stations to ensure the transmission of finite-length packets on a shared channel between subscriber stations connected to this shared channel, optimizes the efficiency of using the bandwidth of the shared channel in the interests of all subscribers of this channel.

 A known method of exchange with time division of the channel of collective use (see. Data transmission systems and computer networks M .: Mir, 1974, p. 60 [1].

 In the known method [1], the transmission of information in a shared channel from each subscriber station is allowed in a strictly fixed time interval for this station.

 The disadvantage of this method should be attributed to the inefficient use of the bandwidth of the channel of collective use with low traffic subscribers.

 A known method of transmitting messages with random access of subscribers to the channel of collective use (see. Scherbo V.K., Kirichev V.M., Samoilenko S.I. Standards on local area networks, M .: Radio and communications, 1990, p. [ 23].

 A known method [23] for transmitting messages is that all stations collectively use a common physical environment, at each station that has data for transmission, they monitor the state of the physical environment and, in the absence of transmissions from other stations, place their message in the physical environment. If, after the start of transmission, the message in the channel collides with the message of the other station, then each of these stations provides a random combination to the physical environment, recognized at each station as false information. The station then waits for a certain, dynamically changing period of time before retrying the transmission.

 The disadvantages of this method [2] include the fact that when it is used, there is a possibility of simultaneous transmission of several subscriber stations (collisions), which leads to loss of information, delays in its transmission. This probability is higher, the higher the intensity of information transfer in local networks.

 Closest to the proposed facility for its intended purpose, technical nature and the achieved result is a method of transmitting packets in a segmented ALOHA system (see TIIER, M .: Mir, Volume 75, N 1, 1987, p. 167 [3].

 In accordance with this method, all subscriber stations are synchronized with each other, the current time is divided into segments of equal duration, if there is information, packets are transmitted in segments allocated for each particular packet station, synchronously so that the beginning of the packet coincides with the beginning of the segment, and the packet is transmitted completely ends during the segment, receive information at all packet stations.

 The disadvantage of this method should be attributed to the inefficient use of the bandwidth of the channel of collective use, especially with low traffic subscribers. The fact is that time segments belonging to subscriber stations that do not have information for transmission remain unused during the entire period of lack of information at these stations. In addition, the amount of information packet transmitted is limited by the size of the segment. Therefore, a slight increase in the amount of information outside the segment will lead to the need to occupy another segment for the transfer of residual information.

 The aim of the invention is to increase the efficiency of using the bandwidth of the channel of collective use at low traffic and the removal of restrictions on the amount of information transmitted in the package. To achieve the objective of the invention, the problem of ensuring the transmission of information in segments of those subscriber stations that do not transmit information at present, uniform distribution of segments of the shared channel between subscriber stations having information for transmission, and the possibility of transmitting packets of arbitrary length are solved.

The invention consists in the fact that to solve the problem at the subscriber station network
- the current time is divided into segments of equal duration T _s (T _s ≥ 2t _p + T _op , where t _p is the propagation time of signals between the two most remote subscriber stations in the local network, t _op is the time of recognizing the presence of a carrier from other stations in the collective channel use accepted in this local network);
- subscriber stations synchronize;
- Assign segments to subscriber stations;
- at each subscriber station, the occupancy of the collective channel is determined by analyzing the carrier;
- in case of occupancy of the collective use channel, the carrier is analyzed and after the release of the collective use channel, the start of the “own” segment is shifted, shifting the entire timeline, by the time the channel is busy;
- if there is information at the subscriber station, it is transmitted in packets of arbitrary length (T _p ) in a synchronous manner so that the beginning of the packet coincides with the beginning of the next segment beyond "your"one;
- the transmission of the packet is completed during the time interval, the value of which is determined as T _p .

The features that distinguish the proposed method from the prototype include the fact that
- at each subscriber station, the occupancy of the collective channel is determined by analyzing the carrier;
- in case of occupancy of the collective use channel, the carrier is analyzed and after the release of the collective use channel, the start of the “own” segment is shifted, shifting the entire timeline, by the time the channel is busy;
- if there is information at the subscriber station, it is transmitted in packets of arbitrary length (T _p ) in a synchronous manner so that the beginning of the packet coincides with the beginning of the next segment beyond "your"one;
- the transmission of the packet is completed during the time interval, the value of which is determined as T _p .

The ability to achieve this goal, namely, to increase the efficiency of using the bandwidth of the collective channel at low traffic, is due to
- with this method of packet exchange time segments (T _c ) are relatively much shorter than in the prototype. Therefore, waiting for the segment in which information will be transmitted takes less time. In addition, all segments are used to transmit information and to determine the ability to start transmitting information;
- in the absence of information for transmission at a packet station, the segments allocated for this station can be used to transmit information from other packet stations;
- each packet station has the ability to transmit its information in the allotted time for it;
- provided the ability to transfer packets of arbitrary length.

 In FIG. 1 shows a structural electrical diagram of a packet station for implementing the proposed method; in FIG. 2 is a timing diagram of dividing a shared network channel of a local network into time segments, allocating segments to subscriber stations of the local network, forming packets when transmitting information from one, two and N transmitting stations; in FIG. 3 - graphs of the efficiency of using the bandwidth of the collective channel for the prototype and the proposed methods.

 The device (Fig. 1) contains a timing unit 1, an access control unit 2, a receiver 3, a microprocessor 4, a transmitter 5.

The proposed method can be implemented as follows. Subscriber stations of the local network are constantly in a state of receiving information from a shared channel. From the moment the subscriber station is connected to the local area network by an exact time signal (for example, from CEB) or another signal common to the given local area network, the timing unit 1 is started, by means of which time intervals T _c , 2t _p and t _{op are formed} (Fig. 2a, b ) and allocate a segment of "their" station. If information is transmitted in the shared channel (that is, the channel is busy) in the receiver 3, the carrier is analyzed and the channel busy signal is transferred to the other input of the timing unit 1, the beginning of “their” segment is shifted, shifting the entire timeline, by the channel’s busy time.

The intervals T _c and t _op allocated at the i-th subscriber station (where i = 1, 2, ..., N) in the control unit 2, to the other input of which from the receiver 3 a signal is received on the presence of a carrier in the shared channel ( channel busy signal), allocate the interval t _op. in the "own" segment T _c , on which the carrier is analyzed (Fig. 2.b). If there is a lack of information in the communication channel for t _op at the “own” interval T _s , an access permission signal is generated at the end of the interval T _s , which is transmitted to microprocessor 4 and determines the possibility of transmitting an information packet from microprocessor 4 through transmitter 5 to the communication channel collective use. In this case, if there is information for transmission, the transmitter 5 is turned on for transmission and the information is transmitted from the microprocessor 4 in packets of arbitrary length in a synchronous manner so that the beginning of the packet coincides with the beginning of the next segment beyond its own. The transmission of the packet is completed during the time interval, the value of which is determined as T _p .

 In FIG. 2.2 is a time chart of the use of a shared channel when transmitting packet information from the 1st subscriber station, FIG. 2.3 is a timing chart for the case of transmission from the 1st and 3rd subscriber stations, in FIG. 2.3 - from all N stations.

 Implementation of the proposed exchange method in a packet network allows to increase the efficiency of using the bandwidth of a collective use channel with low traffic (with the number of operating subscriber stations from 1 to N-1) by providing information transfer in segments of those subscriber stations that do not currently transmit information , uniform distribution of segments of the channel of collective use between subscriber stations that have information for transmission and enable transmission etov arbitrary length. In FIG. Figure 3 graphically shows the possibility of increasing the efficiency of using the bandwidth of a shared channel (C) depending on the number of packet stations (n) transmitting information.

Sources of information:
1. Data transmission systems and computer networks. - M.: Mir, 1974, p. 60.

 2. Scherbo V.K., Kirichev V.M., Samoilenko S.I. Standards for local area networks. - M .: Radio and communications, 1990.

 3. TIIER. - M .: Mir, t. 75, N 1, 1987, p. 167.

Claims (1)

The method of packet exchange in local networks with the collective use of a common physical environment, in which all subscriber stations synchronize with each other, divide the current time into segments and constantly receive information, characterized in that the segment value is chosen equal to T _s ≥ 2t _p + t _op , where t _p - signal propagation time between the two most distant subscriber stations in the local network and the _op t - time identification carrier presence from other stations in the shared channel, received in the local ce and, at each subscriber station, the occupancy of the shared channel is determined by analyzing the carrier, in the case of the occupancy of the shared channel, the carrier is analyzed and after the channel is released, the start of the “own” segment is shifted, shifting the entire timeline by the time the channel is busy, provided it is not detected at the subscriber station in for "their" interval T _with employment shared channel, and there is information to be forwarded to transmit packets of arbitrary length in a synchronous manner, so that the beginning of paragraph chum coincided with the beginning of the following for the "" segment.

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